As pointed out in the Doe et al U.S. Pat. No. 3,918,481, there are circumstances in which faults develop in gas supply lines to commercial or domestic premises; under these circumstances it is of course highly desirable to limit the escape of gas through the fault. For example, if excavation work causes a major tear to develop in a gas supply line which would other otherwise allow a massive and dangerous quantity of gas to escape to the atmosphere, it is essential that the supply of gas upstream from the tear be immediately and automatically restricted. On the other hand, a complete shut-off of gas would make recommissioning of the repaired line difficult, and therefore it is desirable that the automatic shut-off means not completely cut off the flow of gas, but instead cut down the flow to only a very small and controlled amount.
The device of the aforementioned Doe et al U.S. Pat. No. 3,918,481 serves the aforementioned function very well. This prior device, known as the "Donkin.RTM. Flow Limitor" has been sold and used in quantities of over six hundred thousand since 1984, without failure. It has served the industry very well and continues to serve the industry well to this day. Even so, the device of Doe et al U.S. patent does have some defects including a complex construction which makes manufacture costly and installation difficult, and certain performance shortcomings as explained below. Regarding its construction, its nonmodular form requires installation using special tools, and placement of the component parts relative to the compression of the spring is extremely critical and difficult in order to obtain optimum performance.
Regarding performance, the Doe et al flow limitor is not suitable for use in low pressure and/or high capacity, i.e. high flow rate, systems; and therefore the need exists for an improved flow limitor which has a "wider proportional band", i.e. a flow limitor which can handle a greater range of gas flow rates as well as high, normal and low pressure systems. There is a further demand for a flow limitor which is more sensitive, i.e. will trip under a lower pressure drop, thereby providing improved safety performance. Lastly, the Doe et al flow limitor has a complex construction including gaskets and washers, and therefore there is a demand for such a flow limitor which is simpler in construction and therefore less expensive to manufacture and install compared with the aforementioned Doe et al device.
Many valves and regulators exist in the prior art for carrying out a variety of functions relative to the flow therethrough of different kinds of fluids, liquid or gas. One example is shown in the Pittsley U.S. Pat. No. 3,359,960 which discloses a crankcase ventilation valve for controlling the flow of vapors from the crankcase to the induction system of an internal combustion engine. The Pittsley valve is intended and constructed to oscillate between the positions shown in FIGS. 2 and 3 based on rapidly changing differences in pressure between the engine crankcase and the induction system. As shown by the arrows in FIG. 2, the gas flow is from the passage 60, through the valve chamber 52, and then into and through the passage 66. As seen from FIG. 5, when the pressure drops downstream and that pressure drop is transferred through passage 66, there is initially an increase in the flow rate as the head 76 of the plunger 54 moves away from the seat 56, and then there is a gradual decrease in the flow rate as the pressure differential increases and as the plunger 54 enters the central passage 66 as shown in FIG. 3.
A number of other prior patents are of interest, including the Blust U.S. Pat. No. 1,627,312 which discloses an automatic safety cut-off for gas valves. Keller U.S. Pat. No. 1,063,933 shows a gas regulating valve. Sciore U.S. Pat. No. 2,988,346 shows a fuel regulating valve. Sands U.S. Pat. No. 3,122,162 discloses a flow control device. Werding U.S. Pat. No. 4,650,094 is directed to a thrust regulator. Luetzelschwab U.S. Pat. No. 4,510,993 discloses a flow controller. And the Saito et al U.S. Pat. No. 4,075,294 discloses a carburetor control valve.
In general and with few exceptions, it can be said that these prior devices are constructed for different environments and to provide different results. In gas regulator devices of the prior art, the gas flow direction is such that when there is a pressure drop downstream the valve opens to permit an increase flow of gas. In most prior art valves, the construction is such that when the valve is closed flow is stopped entirely.